"Because of the high natural frequency response of the sound fast, high-strength carbon nanotubes is different from the crystal structure of carbon is suitable for precise and delicate sound representation.As one of the important elements to reproduce the treble, the HA-FXZ series, in the twin system unit of one vibration of carbon nanotubes in serving as combination and the optimal bass realistic stream woofer newly developed in one unit has adopted the carbon diaphragm, and the other plate."

So, as mentioned, a carbon diaphragm. I see the reasoning, and matching peoples impressions of the brighter CNT drivers that bring more treble, detail, and clarity improvements which is not what they want for the woofer. So, CNT all the way through is probably not what you want and I believe they made the right choice there. Remember, this is a Kelton sytem where all three work together and there is no crossover. So they used a different material to aid in tuning. IME, with the S900 and M750 carbon drivers, JVC carbon diaphragms are certainly bass focused.

The basic F.R. graphs to illustrate...

Ha ha, red and blue make green. That carbon driver doesn't even know what treble is, lol. All about the bass.